Cost-effective Communication and Control Architectures for Active Low Voltage Grids

University dissertation from Stockholm : KTH Royal Institute of Technology

Abstract: The monitoring and control of low voltage distribution grids has historically been disregarded due to the unidirectional power flow. However, nowadays the electric power system is being modernized to enable a sustainable energy system. This is assisted by the smart grids concept, which incorporates the new types of loads, the active energy consumers, often called 'prosumers', and the higher requirements for reliability and quality of service. The number of prosumers is increasing since many houses, apartments, commercial building and public institutions are beginning to produce energy, mainly through solar photovoltaic panels on their rooftop. These installations are principally promoted by the fall in the cost of renewable energy technologies, especially solar panels. Thus, while the small-scale renewables can reduce the electricity bill for the consumers, they can also generate problems for the distribution grid operators because the non-consumed energy surplus is exported to the grid and that requires updating the existing electricity infrastructures. This new paradigm adds new regulatory, economical, and technical type of challenges. In response to this new situation, this thesis investigates the communication and control architectures that are required for active low voltage grid monitoring and control applications, considering the regulatory constraints and the efficient utilization of the assets from a distribution system operator’s perspective.Hence, this thesis contributes by proposing a framework and optimization studies to assess the required communication and the control solutions (i.e., sensors and actuators) from a cost-effective point of view. This is done by including the economic aspects (CAPEX & OPEX) into the optimization formulation. The communication solutions are twofold: first, the optimal sensor placement configuration that is required to perform low voltage state estimation is covered. Then, the optimal metering infrastructure designs for active low voltage monitoring application are studied. The control solutions are threefold and cover the decentralized and coordinated distribution automation applications: first, control strategies are proposed to allow the integration of microgrid-like structures into the distribution grids. Second, the procedure to optimally place the control actuators (i.e., tap changers) for running the control strategies is studied. Third, a decentralized and multiagent-based control solution is proposed for self-healing and feeder reconfiguration applications. In addition, a framework model and its corresponding simulation tool are developed for studying and assessing the reliability of the ICT infrastructure that enables the active low voltage grid monitoring and control applications.As concluding remarks, the technology readiness level shows that the required communication and control architectures for enhancing the active low voltage grids with new services are mature, as they are for high voltage grids. However, the technological deployment at low voltage grids is restricted to the assets that can only be owned by the distribution system operator. This fact limits the operability and requires solutions that prioritize cost-effectiveness over comprehensiveness and complexity. Thus, the results from the presented studies show that it is essential to perform thorough cost-benefit analysis of the potential improvement solutions for each particular grid, because this will allow deploying the right technology only at the necessary locations.